Enantiomeric inhibitors of cholesterol esterase and acetylcholinesterase

摘要

Enantiomers of N-methyl-N,α-methylbenzylbutyramide (1), 1-butyl-3-methyl-3'-α-methylbenzylurea (2), 1,2,3,4-tetrahydro-1-naphthyl-N-butylcarbamate (3), 1,1'-bi-2-naphthyl-2,2'-di-N-butylcarbamate (4), 1,1'-bi-2-naphthyl-2-ol-2'-N-butylcarbamate (5), 1,1'-bi-2-naphthyl-2-butyrate-2'-N-butylcarbamate (6) are inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of 4-nitrophenyl butyrate and of electric eel acetylcholinesterase-catalyzed hydrolysis of acetylthiocholine in the presence of 5,5'-dithiobis-2-nitrobenzoate. For competitive inhibitors, values of the inhibition constant (K_i) and the enantiomeric ratio (E_(comp.)) are investigated. For active site-directed irreversible inhibitors, values of the inhibition constant (K_i), the carbamylation constant (k_2), the bimolecular rate constant (k_i), and the enantiomeric ratio (E) are investigated. Toward both enzymes, compounds 1 are poor competitive inhibitors (K_i = 10~2-10~4 μM) but have good enantioselectivities (E_(comp.) = 10-50, the preference for R). R-2 and S-2 are competitive inhibitors of acetylcholinesterase with K_i = 26 and 80 μM, respectively (the preference for R) but are active site-directed irreversible inhibitors of cholesterol esterase with k_i = 4 and 16 M~(-1) sec~(-1), respectively (the preference for S). For those competitive inhibitions, both leaving group hydrophilic and hydrophobic binding sites of cholesterol esterase or both anionic substrate binding site and peripheral anionic binding site of acetylcholinesterase bind to N, N-methyl-α-methylbenzyl disubstituted amide parts of these inhibitors and the enzyme does not catalyze the hydrolysis of these inhibitors. The opposite stereopreference (S) for the inhibition of cholesterol esterase by compounds 2 may be due to the fact that N, N-methyl-α-methylbenzyl disubstituted amide parts of these inhibitors bind to the alkyl chain binding site of the enzyme. Compounds 3-6 are active site-directed irreversible inhibitors of cholesterol esterase (k_i = 1-13 000 M~(-1) s~(-1)) and peripheral anionic binding site-directed irreversible inhibitors of acetylcholinesterase (k_i = 1.7-1300 M~(-1) s~(-1)). Compounds 3 have low enantioselectivities (E = 1.3-1.4) for both enzymes. The stereopreference for atropisomers 4 and 6 is S-form toward both enzymes (E = 2-30) and is identical to that of cholesterol esterase-catalyzed hydrolysis of 1,1'-bi-2-naphthyl-2,2'-diacylate. This stereopreference (S) may be due to the fact that the butyryl group or one of two butylcarbamate groups of S-atropisomers binds more effectively to the leaving group hydrophobic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase than that of R-atropisomers. The opposite stereopreference (R) for atropisomers 5 toward both enzymes may be due to a favorable interaction between the hydroxyl group of the inhibitors and the leaving group hydrophilic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase.